package core6502 import ( "encoding/binary" "fmt" "io" ) // https://www.masswerk.at/6502/6502_instruction_set.html // http://www.emulator101.com/reference/6502-reference.html // https://www.csh.rit.edu/~moffitt/docs/6502.html#FLAGS // https://ia800509.us.archive.org/18/items/Programming_the_6502/Programming_the_6502.pdf const ( maxInstructionSize = 3 ) // State represents the state of the simulated device type State struct { reg registers mem Memory cycles uint64 opcodes *[256]opcode trace bool lineCache []uint8 // We cache the allocation of a line to avoid a malloc per instruction. To be used only // by ExecuteInstruction(). 2x speedup on the emulation!! } const ( vectorNMI uint16 = 0xfffa vectorReset uint16 = 0xfffc vectorBreak uint16 = 0xfffe ) type opcode struct { name string bytes uint16 cycles int addressMode int action opFunc } type opFunc func(s *State, line []uint8, opcode opcode) func (s *State) executeLine(line []uint8) { opcode := s.opcodes[line[0]] if opcode.cycles == 0 { panic(fmt.Sprintf("Unknown opcode 0x%02x\n", line[0])) } opcode.action(s, line, opcode) } // ExecuteInstruction transforms the state given after a single instruction is executed. func (s *State) ExecuteInstruction() { pc := s.reg.getPC() opcodeID := s.mem.PeekCode(pc) opcode := s.opcodes[opcodeID] if opcode.cycles == 0 { panic(fmt.Sprintf("Unknown opcode 0x%02x\n", opcodeID)) } if s.lineCache == nil { s.lineCache = make([]uint8, maxInstructionSize) } for i := uint16(0); i < opcode.bytes; i++ { s.lineCache[i] = s.mem.PeekCode(pc) pc++ } s.reg.setPC(pc) if s.trace { //fmt.Printf("%#04x %#02x\n", pc-opcode.bytes, opcodeID) fmt.Printf("%#04x %-13s: ", pc-opcode.bytes, lineString(s.lineCache, opcode)) } opcode.action(s, s.lineCache, opcode) s.cycles += uint64(opcode.cycles) if s.trace { fmt.Printf("%v, [%02x]\n", s.reg, s.lineCache[0:opcode.bytes]) } } // Reset resets the processor. Moves the program counter to the vector in 0cfffc. func (s *State) Reset() { startAddress := getWord(s.mem, vectorReset) s.cycles += 6 s.reg.setPC(startAddress) } // GetCycles returns the count of CPU cycles since last reset. func (s *State) GetCycles() uint64 { return s.cycles } // SetTrace activates tracing of the cpu execution func (s *State) SetTrace(trace bool) { s.trace = trace } // GetTrace gets trhe tracing state of the cpu execution func (s *State) GetTrace() bool { return s.trace } // GetPCAndSP returns the current program counter and stack pointer. Used to trace MLI calls func (s *State) GetPCAndSP() (uint16, uint8) { return s.reg.getPC(), s.reg.getSP() } // GetCarryAndAcc returns the value of te carry flag and the accumulator. Used to trace MLI calls func (s *State) GetCarryAndAcc() (bool, uint8) { return s.reg.getFlag(flagC), s.reg.getA() } // Save saves the CPU state (registers and cycle counter) func (s *State) Save(w io.Writer) error { err := binary.Write(w, binary.BigEndian, s.cycles) if err != nil { return err } binary.Write(w, binary.BigEndian, s.reg.data) if err != nil { return err } return nil } // Load loads the CPU state (registers and cycle counter) func (s *State) Load(r io.Reader) error { err := binary.Read(r, binary.BigEndian, &s.cycles) if err != nil { return err } err = binary.Read(r, binary.BigEndian, &s.reg.data) if err != nil { return err } return nil }